extend File-Formats.md with mutational signature datatype

docs/File-Formats.md

@@ -1609,7 +1609,7 @@ The mutational signature meta files follow the same convention as the [Generic A
 however there are some key differences:
 - `genetic_assay_type` should be set to `MUTATIONAL_SIGNATURE`
 - `stable_id` values should end with: `{datatype}_{identifier}`, where:
-  - `datatype` is one of `contribution`, `pvalue` or `matrix`
+  - `datatype` is either `contribution`, `pvalue` or `matrix`
   - `identifier` is consistent between files belonging to the same analysis
   - Multiple signatures can be added to a single study, as long as they have different identifiers in their stable id (e.g., `contribution_SBS` and `contribution_DBS`)
 - In `generic_entity_meta_properties` the `NAME` value is required. The `DESCRIPTION` and `URL` values can be added 
@@ -1623,7 +1623,7 @@ Each collection of mutational signatures can consist of up to three different da
 - Signature p-values file (optional)
   - Data file containing p-values for each signature-sample pair. Values below 0.05 will be treated as significant.
 - Mutation matrix file (optional)
-  - Data file containing nucleotide changes of a sample. cBioPortal has specific visualisation options for single-base substitutions (96 channels), double-base substitutions (72 channels) and insertion/deletions (83 channels), following the signatures defined by [COSMIC](https://cancer.sanger.ac.uk/signatures/). But other channels can also be used. Values are expected to be positive integers.
+  - Data file containing nucleotide changes of a sample. cBioPortal has specific visualization options for single-base substitutions (96 channels), double-base substitutions (72 channels) and insertion/deletions (83 channels), following the signatures defined by [COSMIC](https://cancer.sanger.ac.uk/signatures/). But other channels can also be used. Values are expected to be positive integers.
 
 ## Resource Data